February, 1941. After months of bombing raids in London, twelve-year-old Olive Bradshaw and her little brother Cliff are evacuated to the Devon coast. The only person with two spare beds is Mr Ephraim, the local lighthouse keeper. Desperate to be helpful, Olive becomes his post-girl, carrying secret messages (as she likes to think of the letters) to the villagers. But Olive has a secret of her own. Her older sister Sukie went missing in an air raid, and she's desperate to discover what happened to her.